Southwest was not the only airline that was profitable [some years] during the last 35 years.
Southwest does little outsourcing ?

Please check the amount of outsourcing they do in aircraft maintenance..
[This is where your [20%] less employees/ aircraft is very deceiving.]
There is no doubt that Southwest is a very well run airline,
But it is my contention it was their fuel hedging [in recent years] is [mainly] what has carried them through some very difficult times in the airline industry.
Maybe not, but they are the only major airline that has been
consistently profitable over the past 35 years. (And with their fleet and their revenue and their market cap and their market share, you can't call them anything other than a major airline. International, no. Major, you bet.)
You must be in a/c maintenance. I notice that when someone blindly focusses on ourtsourceing of maintenance, then they tend to be in a/c maintenance. When they focus on outsourcing of gate and ATO agents, they tend to be in that area.
You keep parroting that SW outsources maintenance, but so does LCC. I don't know (and don't really care) if ANY major airline does 100% of their own maintenance. It is not sensible to do everything when there is someone else who can do the same work for less money.
It is not sensible to have company employees staff a station that gets just a few flights/day. I work for AA. BHM is a contract station because AA has 4 flights/day. The first departure is at 0650. The last arrival (an RON for the 0650) is at 2150. IIRC, ALL of the major airlines,
except SWA, have outsourced their ground personnel at BHM, including LCC.
And, the argument that if they didn't have fuel hedging, they would not have been profitable or as profitable is facetious. It is in the same category of argument as "If my sister were a man, she would be my brother." My sister is not a man, and SWA
did have fuel hedging. So, that ship has sailed.
All you can prove by arguing that SWA has fuel hedging is the fact that SWA has fuel hedging. And, unfortunately for all of the rest of us, they did it better than the rest of us. Just as they have done a lot of things better than the rest of us.